when you see a random hair on your body, you’re probably ... · when you see a random hair on...

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Firefly-Inspired Sensor Network Synchronicity with Realistic Radio Effects Geoffrey Werner-Allen, Geetika Tewari, Ankit Patel, Matt Welsh, Radhika Nagpal Division of Engineering and Applied Sciences Harvard University {werner,gtewari,abpatel,mdw,rad}@eecs.harvard.edu ABSTRACT Synchronicity is a useful abstraction in many sensor net- work applications. Communication scheduling, coordinated duty cycling, and time synchronization can make use of a synchronicity primitive that achieves a tight alignment of individual nodes’ firing phases. In this paper we present the Reachback Firefly Algorithm (RFA), a decentralized syn- chronicity algorithm implemented on TinyOS-based motes. Our algorithm is based on a mathematical model that de- scribes how fireflies and neurons spontaneously synchronize. Previous work has assumed idealized nodes and not consid- ered realistic effects of sensor network communication, such as message delays and loss. Our algorithm accounts for these effects by allowing nodes to use delayed information from the past to adjust the future firing phase. We present an evaluation of RFA that proceeds on three fronts. First, we prove the convergence of our algorithm in simple cases and predict the effect of parameter choices. Second, we leverage the TinyOS simulator to investigate the effects of varying parameter choice and network topology. Finally, we present results obtained on an indoor sensor network testbed demon- strating that our algorithm can synchronize sensor network devices to within 100 μsec on a real multi-hop topology with links of varying quality. Categories and Subject Descriptors C.2 [Computer-Communication Networks]: Network Architecture and Design, Distributed Systems General Terms Algorithms, Design, Experimentation, Theory Keywords Synchronization, Wireless Sensor Networks, Biologically In- spired Algorithms, Pulse-Coupled Oscillators Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. SenSys’05, November 2–4, 2005, San Diego, California, USA. Copyright 2005 ACM 1-59593-054-X/05/0011 ...$5.00. 1. INTRODUCTION Computer scientists have often looked to nature for inspi- ration. Researchers studying distributed systems have long envied, and attempted to duplicate, the fault-tolerance and decentralized control achieved in natural systems. Those of us studying sensor networks also have every reason to be envious. Designing software coordinating the output of a collection of limited devices frequently feels as frustrating as orchestrating the activity of a colony of stubborn ants, or guiding a school of uncooperative fish. And yet ant colonies complete difficult tasks, schools of fish navigate the sea, and swarms of fireflies stretching for miles can pulse in perfect unison, all without centralized control or perfect individ- uals. The spontaneous emergence of synchronicity — for example, fireflies flashing in unison or cardiac cells firing in synchrony — has long attracted the attention of biologists, mathematicians and computer scientists. Synchronicity is a powerful primitive for sensor networks. We define synchronicity as the ability to organize simulta- neous collective action across a sensor network. Synchronic- ity is not the same as time synchronization: the latter im- plies that nodes share a common notion of time that can be mapped back onto a real-world clock, while the former only requires that nodes agree on a firing period and phase. The two primitives are complementary: nodes with access to a common time base can schedule collective action in the future, and conversely, nodes that can arrange collective action can establish a meaningful network-wide time base. However, the two primitives are also independently useful. For example, nodes within a sensor network may want to compare the times at which they detected some event. This task requires a notion of global time, however it does not require real-time coordination of actions. Similarly, synchronicity by itself can be extremely useful as a sensor network coordination primitive. A commonly- used mechanism for limiting energy use is to carefully sched- ule node duty cycles so that all nodes in a network (or a por- tion of the network) will wake up at the same time, sample their sensors, and relay data along a routing path to the base station. Coordinated communication scheduling has been used both at the MAC level [18] and in multi-hop routing protocols [12] to save energy. Synchronicity can also be used to coordinate sampling across multiple nodes in a network, which is especially important in applications with high data rates. Previous work on seismic analysis of structures [1], shooter localization [13], and volcanic monitoring [15] could use such a primitive and avoid the overhead of maintaining consensus on global time until absolutely necessary.

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Page 1: When you see a random hair on your body, you’re probably ... · When you see a random hair on your body, you’re probably tempted to pull it out. After all, it’s a hair out of

When you see a random hair on your body, you’re probably tempted to pull it out. After all, it’s a hair out of place and it’s right there. But experts say you should take a beat before getting pluck-happy.

That's because shen you pluck a hair with tweezers, it pulls the hair shaft from the skin at its root, says Joshua Zeichner, M.D., a New York City-based board-certified dermatologist. “While there may be some degree of inflammation in the hair follicle from tweezing, generally tweezing is not considered a form of permanent hair removal and a new hair will be produced,” he says. But you can also traumatize or scar your skin, causing permanent damage in the area, which is why it’s best to proceed with caution.

“It really depends on the location,” says Gary Goldenberg, M.D., medical director of the Dermatology Faculty Practice at the Icahn School of Medicine at Mount Sinai.

These are the areas experts say you should think twice about before tweezing:

Page 2: When you see a random hair on your body, you’re probably ... · When you see a random hair on your body, you’re probably tempted to pull it out. After all, it’s a hair out of

Sure, you probably tweeze your brows all the time, but eyebrow hair is very sensitive to trauma and repeated tweezing can produce permanent damage to the hair follicle, Goldenberg says.

"Trimming or waxing is better," says Goldenberg. But he warns that waxing can also thin eyebrows permanently. Basically, if you’ve been rocking super-thin eyebrows for years and suddenly decide you want to channel Cara Delevingne, it might be harder than if you had just let your brows be all along.

Page 3: When you see a random hair on your body, you’re probably ... · When you see a random hair on your body, you’re probably tempted to pull it out. After all, it’s a hair out of

If you must pluck a nipple hair, it’s best to make sure that there’s at least one to two millimeters of growth before

tweezing. “Otherwise the tweezer itself may cause trauma to the skin in your attempt at grasping at a very short hair,”

Zeichner says. Just know this: There is a chance you could cause an infection, so proceed with caution. Trimming is a

better option here.

Having hair coming out of a mole looks a little weird, but plucking it can cause inflammation and a possible infection,

Goldenberg says. “It’s best to avoid tweezing,” he says. “Trimming or laser hair removal are much safer and can

produce more permanent results.”

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It’s pretty common to develop a pus pimple around a hair, Zeichner says, and it’s usually a form of folliculitis (a mild infection around the hair shaft) rather than legit acne. “While plucking the hair, which removes pus along with it, can help clear up the infection, you should apply an antibiotic appointment as well, such as over-the-counter bacitracin ointment,” he says, noting that trying out a drying gel with salicylic acid can be helpful as well.

However, if it really is a pimple, you could do even more damage, up the odds that you’ll get bacteria in there, and increase the chances that you’ll get a scar, Goldenberg says. Plus, it will really, really hurt. So be warned! (We recommend this soothing natural combo mask and spot treatment to deal with breakouts.)

Ingrown hairs suuuck, but it’s not a good idea to tweeze them. “It increases the risk of infection and can cause scarring in the area,” Goldenberg says. Instead, he says it's best to apply a warm compress or see your dermatologist to make sure the area does not need to be drained.

So, when in doubt, chill out on plucking your hair. Everyone has hairs in weird places, and it’s really not a big deal. However, if it really bothers you, try trimming it or see your dermatologist for help.